Document Skia in Android

Issue description

Our Skia developer community is often asking questions or expecting the Skia built into the Android platform to be of a certain level or accessible to them. We should to do a better job documenting the Skia that is included in the Android platform vs Chrome vs standalone.
I'll take this item but wanted to open an issue to come back to as I'm working on another focus area in our doc/pages right now.